The present invention relates to a cleaning apparatus used in manufacturing a semiconductor device, and more particularly, to a semiconductor wafer cleaning apparatus which efficiently removes contamination generated during a cleaning process.
In general, as a semiconductor device becomes more integrated, fine particles remaining on the surface of a wafer tend to increasingly impair the characteristics of the device.
Therefore, wafer cleaning techniques for removing the fine particles contained on the surface of the wafer have become increasingly important in manufacturing semiconductor devices.
Current large scale integrated circuit (LSI) technology is capable of mass producing devices having pattern dimensions of about 2 .mu.m. A process of making these very fine devices requires an ultra-clean environment, and therefore, requires surface processing and cleaning techniques for maintaining a clean environment.
FIGS. 1a and 1b are schematic diagrams of conventional semiconductor wafer cleaning apparatus.
FIG. 1a illustrates an over-flowing bath system which includes an internal cleaning tank 1 for cleaning wafers 8. The internal cleaning tank 1 has an inlet 3 for introducing a cleaning solution. The inlet 3 is located at the lower central portion of the internal cleaning tank 1. An external cleaning tank 2 surrounds the internal cleaning tank 1 and has an outlet 4 for removing the cleaning solution from the space surrounding the internal cleaning tank 1. A circulation pipe 10 connects inlet 3 with outlet 4, and a circulation pump 5 is disposed in the circulation pipe 10 for circulating the cleaning solution. A filter 6 is also provided for filtering the cleaning solution circulated by circulation pump 5 thereby providing filtered cleaning solution to the internal cleaning tank 1 via inlet 3.
The cleaning operation of the over-flowing bath system having the aforementioned configuration will now be described.
First, the cleaning solution is driven by the circulation pump 5 to pass through the filter 6 and into the internal cleaning tank 1 via inlet 3.
Then, wafers 8 are fixed in a cassette 7 and dipped into the cleaning solution.
At this time, fine particles existing on the surface of wafers 8 are cleaned by the circulating cleaning solution flowing through the spaces between the wafers 8.
In other words, the wafers 8 react chemically with and are also mechanically cleaned by the cleaning solution, producing a simultaneous cleaning and etching action.
FIG. 1b illustrates a down-flowing bath system, which includes an internal cleaning tank 1 for cleaning wafers 8. This apparatus locates the outlet 4 for removing the cleaning solution in the central bottom portion of internal cleaning tank. An external cleaning tank 2 surrounds the internal cleaning tank 1 and has inlets 3 for introducing cleaning solution into the space between the internal and external cleaning tanks. A circulation pipe 10 connects inlets 3 with outlet 4, and a circulation pump 5 is connected in the circulation pipe 10 and circulates the cleaning solution. A filter 6 filters the cleaning solution circulated by circulation pump 5. A baffle plate 9 is disposed in the lower portion of the internal cleaning tank 1 and supports a cassette 7 containing wafers 8. The baffle spaces the cassette from the bottom of the internal cleaning tank 1.
First, the cleaning solution is pumped through the filter 6 of the circulation pump 5 to fill the external cleaning tank 2 via inlets 3.
Then, cassette 7, containing wafers 8, is placed on the baffle plate 9 of internal cleaning tank 1. Wafers 8 are then cleaned by the circulating cleaning solution flowing downward through the internal cleaning tank.
The cleaning solution filtered by filter 6 is recirculated back to internal cleaning tank 1 in which wafers 8 are positioned.
The aforementioned conventional cleaning apparatuses, however, are prone to certain problems.
For example, in the over-flowing bath system having an inlet in the lower portion of an internal cleaning tank, the cleaning solution flows upwardly, and fine particles may be dislodged from the wafers by the upward flowing cleaning solution. Several of the particles, however, are of such a size that the force of gravity and the force of the flowing solution cancel each other out, causing the particle to remain in the region where the wafers are positioned. These particles may be dislodged from one portion of a wafer only to stick to another portion of the wafer or they may contaminate other wafers.
In the down-flowing bath system, the upper portion of internal cleaning tank is open so that the cleaning solution flows downwardly. Thus, fine particles, which may have been dislodged during the initial installation of the cassette or during the cleaning process, may float to the top only to be reattached to the wafers as the cassette is lifted out of the solution. Dislodged particles may also stick to other portions of the wafers or contaminate other wafers during their movement between the respective wafers toward the lower outlet.
Therefore, in the conventional cleaning apparatus, the subsequent processes do not consistently and completely clean the wafers, which lowers the yield and adversely affects their characteristics.